In the process of manufacturing thermoplastic bags or other containers including a thickened closure or other section comprised of a thermoplastic material, it is required to take strips of the material and seal peripheral portions thereof to form the enclosure comprising the bag. At the time the side seals of the bag are formed, the material is commonly cut from a web of material by the same element which does the sealing.
The "cutter/sealer" element is normally a metallic alloy wire which prior to this invention had customarily been of a circular cross section. To cut through and seal both the main body and thickened sections of the thermoplastic material, such as a polyethylene resin, the wire would be heated to about 400.degree. Fahrenheit above the degradation temperature of the thermoplastic material. Degradated polymer which is created by contact of the material with the hot wire can create a wax on the sealing equipment reducing its efficiency and requiring frequent shutdown for cleaning. It can also contaminate the product. Production lines customarily have been shut down 10% of the time just for removal of wax build-up on the sealing equipment.
A circular cross-sectioned wire has been employed in the past because it is generally available and because it is the best cross section for avoiding twisting, sagging and vibratory action, the latter sometimes resulting in shorting between the wire and the rest of the sealing equipment. It also provides a more uniform heat gradient throughout the cross section. However, because of its rounded profile, the circular cross section does not melt and pierce as well as a wire which would have a sharper edge approaching the film to be cut and sealed, resulting in an excessive wax build-up. It has been found that changing the shape of the wire can provide the opportunity to significantly reduce the wax build-up.